<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
        function fun(num) {
            if(num <=1){
                return 1;
            }else {
                return num * fun(num-1);
            }
        }
       var newFun = fun;



        console.log('fun(5) :', newFun(5));

    </script>
</body>
</html>